The present invention relates to a recording apparatus, such as an ink jet printer, which includes a drive gear coupled to a power source, a transmission gear for transmitting power to other rotary members, and a clutch device for selecting permission or prohibition of power transmission between the drive gear and the transmission gear. The invention also relates to a sheet feeder for feeding printing sheets incorporated in such a recording apparatus.
In the specification, the “recording apparatus” includes a recording apparatus, such a printer, a copying machine and a facsimile, in which an ink jet recording head is used, and the recording head which ejects ink to a recording medium to perform recording, and also includes a liquid jetting apparatus in which a liquid jetting head corresponding to the recording head which ejects liquid, instead of the ink, selected for its use to a medium corresponding to the recording medium, whereby the liquid sticks to the medium.
Examples of the liquid jetting heads are the recording head mentioned above, a coloring material jetting head used for manufacturing color filters in use for a liquid crystal display or the like, an electrode material (conductive paste) jetting head used for forming electrodes of an organic EL (electro luminescence) display, a field emission display (FED) and the like, an organic material jetting head used for manufacturing biological biochips, and a sample jetting head as a micro pipette.
One kind of the recording apparatus is an ink jet printer (referred to as a “printer”). Some types of printers are each provided with an auto sheet feeder (ASF) for feeding a recording sheet which is one kind of the recording medium, toward an ink jet recording head. The sheet feeder includes a feeding roller for feeding recording sheets. It is a common practice that for the purpose of cost reduction, a drive source for the feeding roller is also used for a drive source for a transporting roller for transporting the recording sheets to the ink jet recording head. In the description to follow, the recording sheet will be used as a typical example of the recording medium. Accordingly, “feeding”, “feeder”, and “feeding roller” will be referred frequently to as “sheet feeding”, “sheet feeder”, and “sheet feeding roller”, respectively.
When power is transmitted from a drive motor as the drive source to the transporting roller and the sheet feeding roller, for example, when the recording sheet is transported by the transporting roller, it is necessary to stop the rotation of the sheet feeding roller. Further, it is necessary to forwardly and reversely rotate the transporting roller. In this respect, as disclosed in Japanese Patent Publication No. 10-329965A, a clutch device is provided which selects permission or prohibition of power transmission from the drive motor to the sheet feeding roller.
A trigger for selecting the permission or prohibition of power transmission by the clutch device is normally at one end of the main scan direction of a carriage, viz., one end of the main body of the printer as horizontally viewed. The carriage is moved to a position of the trigger located at one end of the scanning path of the carriage, and pressed against the trigger, whereby the clutch device is readily operated.
Since the trigger is provided at only one end of the scanning path of the carriage, when the carriage is positioned at the other end of the scanning path at the end of the recording operation and just before the clutch device is subjected to the selection of the permission or prohibition of power transmission, the carriage must be moved to the position of the trigger over substantially the entire recording region in order to actuate the clutch device. Thus, the carriage consumes time only for traversing the recording region. This time consumption hinders improvement of the throughput from the sheet feeding to the sheet discharging in the recording operation by the printer.
In a technique that the carriage per se engages with a part of the clutch device through the scanning movement to thereby select the permission or prohibition of power transmission to the sheet feeding roller (in other words, the carriage per se serves as a trigger). Sometimes, a position of the carriage when the permission of actual power transmission is switched to its prohibition or permission somewhat varies depending on the dimensional or assembling accuracy of the components.
Upon start of rotation of the sheet feeding roller, various sheet feeding operations are performed during a period of one rotation of the sheet feeding roller. For example, after the sheet feeding roller is rotated by a predetermined angle, the ascending operation of the hopper starts. After the sheet feeding roller is further rotated by a predetermined angle, for example, a retracting operation of a sheet returning lever for returning multi-feeding print sheets to the upstream side is performed. Thus, operation timing charts of components forming the sheet feeder are determined with respect to a rotation start point of the sheet feeding roller. A sequence of sheet feed controls are executed according to the timing charts.
As described above, a position of the carriage when the permission of actual power transmission is switched to its prohibition or permission, varies depending on the dimensional or assembling accuracy of the components. Accordingly, the rotation start point of the sheet feeding roller on which the operation timings determination is based is different for each printer, and hence, exact sheet feed controls are not secured.